1. Field of the Invention
The present invention relates to a feeding device that includes a suction conveying unit and that is installed in electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, or ink-jet printers, and relates to an image forming apparatus that includes the feeding device.
2. Description of the Related Art
Electrophotographic image forming apparatuses, such as copiers, include a feeding device. A bundle of sheet-like recording media (hereafter, simply referred to as “sheets”), such as papers or OHP films, is placed on a sheet placement unit, and the feeding device feeds the sheets one by one to a developing device. The feeding device includes a separation mechanism to separate the sheets from one another in order to prevent multi feeding, i.e., prevent a sheet from overlapping with another sheet when they are supplied.
A friction separation system is widely used in the separation mechanism, where a sheet conveyed from the sheet placement unit by a pick-up roller is separated and delivered due to a frictional force. In the friction separation system, the combination of a separation roller and a friction pad, the combination of a separation roller and a reverse roller, or the like, is used to separate sheets.
As the feeding devices that do not use the friction separation system, air-separation feeding devices described in, for example, Japanese Patent Application Laid-open No. 2001-247229 or Japanese Patent Application Laid-open No. 2007-45630 are known. In the air-separation feeding devices, when air is discharged to the bundle of sheets that is placed on the sheet placement unit in a stacked manner, the sheets are moved, floated, and separated from one another and thus the sheet located at the top sticks to a suction belt due to the suction force (negative pressure) while it is conveyed.
FIG. 12 illustrates the schematic configuration of an air-separation feeding device. An air-separation feeding device 301 illustrated in FIG. 12 includes a tray 302 on which a bundle of sheets P is placed; a front blower 303 and a side blower 304 that blow air to the upper front end and the upper side ends of the placed sheets P; and a rubber suction belt 305 that individually suctions and conveys the sheet P located at the top. The sheets P are aligned on the tray 302 depending on the size of the sheets P such that the front edge of the sheet P is brought into contact with a front fence 306 that is a reference plane.
In order to deliver the sheet P in the air-separation feeding device 301, the front blower 303 and the side blower 304 first blow air to the bundle of sheets P that is placed on the tray 302 so as to apply the air into the gap between the sheets P, whereby the sheets P are moved and floated up to a height h of the suction belt 305. The sheet P1 that is located at the top of the floated sheets sticks to the suction belt 305 and, in this state, the suction belt 305 is rotated so that the sheet P1 is conveyed to an undepicted image forming unit for image formation.
The air-separation feeding devices described in Japanese Patent Application Laid-open No. 2001-247229 and Japanese Patent Application Laid-open No. 2007-45630 include an upper-surface position detection unit that detects the position of the uppermost surface of the placed sheets. The upper-surface position detection unit includes, for example, an actuator 310 that is illustrated in FIG. 12 and is swingably brought into contact with by a fore-end 312 thereof the uppermost surface of the bundle of sheets; and a swing detection sensor 311 that detects swing of the actuator 310. The actuator 310 is installed in a position close to the suction belt 305 so as to keep the target distance h with a stabile accuracy regardless of the size of sheets.
When the height of the bundle of sheets is decreased after a sheet is delivered, the actuator 310 is accordingly swung. The swing detection sensor 311 then detects the degree of swing of the actuator 310 and, in accordance with the detection signal, a bottom plate 302a of the tray 302 is lifted up by an undepicted lifting unit so that the height (distance) h from the upper surface of the bundle of sheets to the suction belt 305 is controlled to be constant.
If paper particles, or the like, of sheets adhere to the surface of the suction belt 305 due to long-term usage, the suction force of the suction belt 305 is decreased and thus improper feeding (no feeding) sometimes occurs. The foreign matter that adheres to the suction belt 305 includes not only paper particles and a loading material of papers but also components of a coating material of coated papers, powders for reprint papers (blocking powders in order to prevent an image from being transferred to the back side of a sheet on which offset printing has been performed), or the like.
(1) in order to remove foreign matter from the suction belt, it is possible that, for example, a brush or scraper is pressed against the suction belt, as described in Japanese Patent Application Laid-open No. 2012-25491, Japanese Patent Application Laid-open No. 10-297783, or the like. However, there is a higher possibility that, if the removed foreign matter adheres to the sheet that is to be delivered, images are improperly formed due to the foreign matter or the foreign matter is mistakenly detected as a sheet; thus, a sheet jam, or the like, occurs.
(2) if a foreign-matter removing member, such as a brush or scraper, is always in contact with the suction belt, the suction belt is abraded due to the contact with the foreign-matter removing member, or the drive resistance of the suction belt is increased. Furthermore, if the foreign-matter removing member is in contact with the suction belt for a moment, a removing operation is not performed in a stable manner.
(3) if the foreign-matter removing member is installed in the feeding device, the costs are increased. Furthermore, if the feeding device does not have any space for installing the foreign-matter removing member, it is difficult to install the foreign-matter removing member.
(4) There is a possibility that, even if foreign matter is removed from the suction belt, the foreign matter adheres to the sheet again or the foreign matter has effects in another way (e.g., the foreign matter is mistakenly detected as a sheet).
(5) if it takes too long to remove foreign matter from the suction belt, the printing productivity is decreased.
(6) If the foreign-matter removing member is deteriorated, the foreign-matter removal performance is decreased; therefore, the foreign-matter removing member needs to be replaced on a regular basis. However, in some configurations where the foreign-matter removing member is installed in the feeding device, it is inconvenient to replace the foreign-matter removing member; thus, the printing productivity and the user convenience are further decreased.
(7) Even if the foreign matter removed from the suction belt is discharged into a place that does not affect image formation, an area near the discharge place is contaminated with foreign matter.
(8) If the frequency at which the cleaning mode of the suction belt is performed is manually increased or decreased to the minimum required frequency in order to improve the printing productivity, and if the frequency is unexpectedly lower than the minimum frequency, the amount of foreign matter, such as paper particles, that adheres to the suction belt is continuously increased; thus, there is a higher possibility that the above-described failures, such as improper images or sheet jams, occur.
(9) In a case where the frequency at which the operation to remove foreign matter is performed is automatically set to the minimum required frequency, i.e., the operation to remove foreign matter is performed each time a predetermined number of sheets are supplied, there is a possibility that, if the setting is not appropriate, a properly cleaned state cannot be obtained. Furthermore, as the abrasion or degradation of the suction belt or the foreign-matter removing member is inevitable, it is necessary to gradually decrease the above-described set number of sheets with time instead of fixing the number.
The present invention has been made in consideration of the foregoing problem and has an object to reduce the abrasion of the suction belt, which is a suction conveying unit, and loss of the drive force of the suction belt, to ensure that paper particles removed from the suction belt are captured and collected without being scattered around the area, and to prevent the paper particles from adhering to the suction belt or the sheet again. The other objects of the present invention are explained with reference to the embodiment described below.